Where It All Goes Down
There's a lot of vegetation in this poem (trees, zinnias, elephant ears), but we're pretty sure "The Whipping" doesn't take place in a forest, even though it kind of seems like it sometimes. Actually, you could probably say the whole scene goes down in some metaphorical jungle. The woman is like a hunter pursuing her prey (the boy) through all kinds of bushes and plants. When she's done whipping him, she rests and licks her chops—well, sort of.
In reality, this poem takes place in some kind of house or apartment, but one that has lots of plants in it (zinnias, elephant ears, and a tree). Okay, it's possible that the poem takes place in the yard, and not in the house or apartment per se, but any way you slice it, it takes place somewhere where the speaker can see everything (we like to think of him as a neighbor).
While this apartment-house-yard-metaphorical forest is the primary setting of this poem, it is not the only setting. In the fourth and fifth stanzas, there is a little flashback-time travel episode. The setting of this violent memory also seems to be a house or apartment, and it too is incredibly violent. It isn't clear if the memory belongs to the speaker or the woman, but it is very unsettling nonetheless.
Ultimately, the most important thing about this poem is that there are two settings, and the poem jumps from one (the present) to the other (the past) and then back again. Strangely, both settings are incredibly violent and unpleasant. The past and the present, the whipping and the memory of the "bony vise," are almost the same thing. This makes sense in a poem that is all about how violence breeds more violence, and how history repeats itself.